Identify duplicate packages and how to eliminate them

We already did a great effort of removing duplication in Dapper, but some is still left, and some more has accumulated again. We should identify candidates and discuss how to get rid of them. E. g. for some packages it is nontrivial to migrate (db4.x if a package uses on-disk transactions, etc.)

Some good candidates: openssl097, gnutls12, libtasn1-2, db4.x, gtk/glib 1.2, more to come.